As displays of mobile applications typified by, for example, smartphones, large-screen liquid crystal display devices have recently been spreading rapidly. Such displays employed in mobile devices have shown a trend toward large-screen and high-definition display in light of capacity of displayed information and screen visibility.
However, such mobile devices, which are mainly in the manner of being held and operated in an operator's hand, preferably have as small a size of the device itself as possible, resulting in that the peripheral area other than the display area (display surface) is required to have an area reduced as small as possible.
To meet this requirement, low-temperature polysilicon (LTPS) liquid crystal display devices in which a display area driving circuit is incorporated in the substrate have recently been increasingly employed, in which the peripheral area other than the display area has a significantly reduced area compared to amorphous silicon (a-Si) liquid crystal display devices that require many driving ICs to be provided outside the glass substrate, composing the mainstream of current mobile device displays.
On the other hand, display devices even using low-temperature polysilicon need input of a driving signal, which in turn requires an additional space for folding of a flexible printed circuit (FPC) board connected to a connecting portion and arranged to supply, for example, an external signal and a power supply voltage, in the connecting portion often set mainly closer to the lower side of the quadrilateral display area. That is, the flexible printed circuit board, which is used for connection with an interconnection formed on the array substrate, is usually required to be folded by 180 degrees on the back side in order to be connected with an external signal source existing on the back side of the substrate so as not to impact the display, resulting in an increase in the external signal interfacing area by the space required for folding.
In addition, the connecting portion of the flexible printed circuit board is exposed on the display side and it is therefore necessary to avoid interference between a protective glass and/or a touch panel glass, which are needed for incorporation into actual mobile application sets such as smartphones, and the connecting portion, placing many restrictions on, for example, the position, thickness, and design of the flexible printed circuit board.